Prepare the raspberry dust. Add 1 cup of the freeze-dried raspberries to a food processor and blend into a fine powder. Set aside.
Melt the ganache base. Place the finely chopped white chocolate and butter in a heatproof bowl. Bring the heavy cream just to a simmer on the stove, then pour it over the white chocolate mixture.
Stir and flavor. Let the bowl sit undisturbed for 2-3 minutes to melt, then stir until smooth. Stir in the raspberry powder until fully incorporated.
Chill. Chill the mixture in the fridge for 1-2 hours, or until firm enough to scoop.
Shape the truffles. Scoop and roll the chilled mixture into small balls. Place them on a baking sheet lined with parchment paper and refrigerate for 20 minutes to firm up.
Dip and finish. Melt the bittersweet chocolate. Dip each cold truffle, letting the excess drip off. Immediately crush the remaining ½ cup of freeze-dried raspberries and sprinkle them on top before the chocolate sets. Chill until firm.
Notes
Storage: Keep these in the fridge in an airtight container for up to 5 days. You can also freeze them for up to 1 month. Doubling the recipe: If you double this for gifts, pour the warm ganache into a shallow 9x13 dish to chill. This increases surface area so the center sets properly.Nutrition info is per truffle